The invention relates generally to an improved aircraft flight instrument sensor that can be used to mitigate or avoid encounters with turbulent or hazardous airflow during routine aircraft flight operations. Direct sensing of a specific component of total measured airspeed is accomplished, taken from instantaneous longitudinal airspeed, mean airspeed, total turbulence, and turbulent cross-components, thus a particular hazardous component is directly sensed, rejecting all other airstream variations. Knowledge of the disturbed air condition to either side of the aircraft is made available to the pilot. The approach is not complex, uses no moving parts, is economical and is easily installed.
Most, if not all, measurements of the airstream from operating aircraft are done by transducers mounted near the fuselage nose or on the vertical fin, as opposed to out on the wing. Among the usual parameters, such as total pressure or impact pressure, static pressure, total temperature, angle-of-attack, and the like, angle-of-attack can be used to determine the vertical component of impinging airflow. Many angle-of-attack transducers are electromechanical in design and U.S. Pat. No. 3,077,773 presents an overview of the measurement together with angle-of-attack and yaw-angle computation. A combination of electromechanical attitude sensing vanes with pitot-static pressure sensing for both air-stream incidence angle and airspeed measurement is taught by U.S. Pat. No. 4,184,149. Aircraft meta-center (center of motion) mounted accelerometers are customarily used to determine three-dimensional accelerations of the aircraft from which indirect determinations of impinging air mass motion may be computed. Such indirect sensing is limited by the narrow bandwidths involved and by airframe non-linear responses to dynamic airstream inputs. Disturbance threshold low energy level skirt signals are simply not able to be measured because of the limited dynamic range of meta-center located instrumentation and airstream input forcing function modification by the flexible airframe, suggesting that many of the published data respecting turbulence encounters may be understated as a result of input signal attenuation by the airframe itself. Little has been done respecting fast response direct sensing and differential measurement across the wingspan since USAF xe2x80x9cProject Jet Streamxe2x80x9d in the 1950""s and early 1960""s, a program to detect jet stream location from an aircraft. The advent of the highly successful xe2x80x9cTIROSxe2x80x9d observational satellites effectively ended all aircraft direct sensing activities by the Government and by the world-wide aviation community. It is subsequently taught in U.S. Pat. No. 5,639,964 that a pair of wing-tip mounted turbulence sensors can determine sharp energy gradients, information which may be useful to the pilot in turbulence avoidance. Sensitive fast response airspeed gust component transducers of the thermal anemometer type disclosed by U.S. Pat. No. 6,134,958 can be used to detect near-instantaneous airstream disturbances.
When a disturbance is encountered head-on by an aircraft the result is usually a sharp jolt or pronounced bounce. If a disturbance is initially encountered by a wing-tip the result can be a hazardous rolling-moment. It is notable that in-trail wake-vortex encounters at altitudes up through cruising altitudes can result in forces sufficient to induce unwanted aircraft roll into the direction of the encounter. It has been observed and reported by NASA Ames Research Center (xe2x80x9cOverview of Wake-Vortex Hazards During Cruisexe2x80x9d by V. J. Rossow and K. D. James, AIAA Paper No. 99-3197) that certain aircraft upsets earlier thought to be caused by clear air turbulence may actually have been encounters with persisting jet aircraft wake-vortices. Their conclusion suggests that all aircraft flight paths could be computer-stored in real time and their tracks, with trailing wake-vortex positions, made available on demand to any other aircraft to facilitate avoidance. Such an approach can be cumbersome and quite costly. The instant invention discloses an easily installed low-cost approach that provides the pilot with immediate knowledge of the energy condition of the local air mass through which he is flying. Pilot awareness of his aircraft""s approach to a disturbance through its threshold skirt region can enable him to take appropriate evasive action to mitigate the effect of the disturbance encounter.
The instant invention discloses an improved combination of airspeed transducer apparatus to form a system where a pair of near-identical sensitive fast-response airspeed gust component transducers is mounted symmetrically, left and right, on or suspended from an aircraft""s wing, each gust sensor feeding the absolute-value of low-pass filtered sensed airstream gust cross-component signals to a difference amplifier. The difference amplifier provides an electrical indication when one side of the aircraft xe2x80x9cseesxe2x80x9d disturbed or turbulent air as may be encountered when an aircraft trailing wake-vortex is approached. When both wingtips simultaneously xe2x80x9cseexe2x80x9d the same disturbed air mass the difference amplifier output signal is nil or zero. As step function changes do not exist in the atmosphere, atmospheric disturbances are surrounded by a threshold region with diminishing energy skirts as you move away from the disturbance. When a wing-tip encounters the skirt region or threshold region of disturbed air the difference output signal will increase, identifying the left or right wing-tip first entering the disturbed air.
When seeking a turbulence component the taking of differences between large longitudinal airspeed values is difficult at best. The thermal anemometer double-element sub-bridge rejects longitudinal or mean airspeed, seen as a common-mode signal, allowing us to look only at the desired instantaneous gust cross-component. The desired component, vertical or horizontal, is determined by airspeed transducer axial orientation as described by U.S. Pat. No. 6,134,958. A turbulent airspeed cross-component is generally bipolar and wing tip-to-tip differences are more readily determined when the cross-component signal is rectified by an absolute-value amplifier. This enables the taking of differences between like polarity signals. Since both airspeed component measurement transducers must be as near-identical as possible, a low-pass filter is placed before the absolute-value stage to control signal bandwidth. This assures similar transducer-to-transducer turbulent energy frequency response. Turbulence frequency range of interest is taught by U.S. Pat. No. 5,639,964. It is important that the wing-tip mounted gust sensor follows rapid turbulent airspeed variations as they occur.
Processing the turbulent or gust component signals in this manner uses the least number of electrical parts. The stages through the absolute-value amplifier stage can all be contained within the transducer support housing itself. The output signal, taken to the difference amplifier which may be located in the fuselage, is a low-source-impedance high-level signal. Alternatively, each wing-tip transducer can contain the system output difference amplifier, only one of which will be actively used, keeping all transducers interchangeable, both physically and electrically. This eliminates the need for a separate physical housing for the difference amplifier.
Use of one transducer per wing half is shown. It should be noted that additional transducers can be added to each wing half provided that symmetry is maintained from side to side. Distribution of an array of transducers along the wing span facilitates profiling and identification of the disturbance type from wing-tip to wing-tip. Their outputs can be summed or added together prior to further signal processing as herein disclosed. In this manner some control can be introduced respecting the scale of sensed disturbance that is detected.